Confused about Cut and HCA correlation?

[ladyleonine]

Newbie here, when doing a bit of research I assumed that an Excellent HCA score = Ideal Cut = beautiful firey sparkle.

But looking at this diamond, for example (waiting for photo and idealscope image, but I like the strong fluorescence )

http://www.jamesallen.com/diamonds/I-VS2-Ideal-Cut-Round-Diamond-1429488.asp

GIA report only grades the cut as Very Good, whereas the HCA score is 0.9 Ex (VG-Ex-Ex-Ex)

What would have brought the GIA grade down? and would the high HCA score be a better indicator of performance?

Also, if a H&A cut is 'perfect' then why do H&A diamonds seem to score higher than 2 on the HCA scale?

many thanks...

 

[ladyleonine]

Another example here:

http://www.jamesallen.com/diamonds/J-SI2-Ideal-Cut-Round-Diamond-1427210.asp

HCA = 1.6 EX (VG-Ex-Ex-VG)
GIA Cut Grade = Very Good

Which should I put more faith in?

 

[Garry H (Cut Nut)]

Another example here:

http://www.jamesallen.com/diamonds/J-SI2-Ideal-Cut-Round-Diamond-1427210.asp

HCA = 1.6 EX (VG-Ex-Ex-VG)
GIA Cut Grade = Very Good

Which should I put more faith in?

That stone was downgrade by GIA because it has a thick girdle.
On the angles and table size it would get GIA Ex

 

[Garry H (Cut Nut)]

Newbie here, when doing a bit of research I assumed that an Excellent HCA score = Ideal Cut = beautiful firey sparkle.

But looking at this diamond, for example (waiting for photo and idealscope image, but I like the strong fluorescence )

http://www.jamesallen.com/diamonds/I-VS2-Ideal-Cut-Round-Diamond-1429488.asp

GIA report only grades the cut as Very Good, whereas the HCA score is 0.9 Ex (VG-Ex-Ex-Ex)

What would have brought the GIA grade down? and would the high HCA score be a better indicator of performance?

Also, if a H&A cut is 'perfect' then why do H&A diamonds seem to score higher than 2 on the HCA scale?

many thanks...

I am not aware that anyone has or should have ever said that all H&A's are 'perfect' ?
Of the 2 stones you can see this one has close to the same spread as the other.
In most lighting it would appear larger.
Also I think the GIA scan on the 1.01ct stone indicating a star facet of 55% is not accurate - It looks closer to 60% to me and there would be some outer facet leakage (something HCA can not pick up because I have not drilled dowwn to that level).

Many slightly deep H&A's stones up to 2.5 and maybe even 3.0 can be quite nice because the tight symmetry will protect from many little worries. But you should be requesting Ideal-scope images to be sure.

 

[ladyleonine]

thanks for that.

Re: H&A 'perfection': the bricks & mortar jewellers I've been to here in Australia and James Allen have all said that the H&A has close to perfect symmetry/ is better than an Ideal cut. Just curious as to why they score lower on HCA, but you've explained it well

 

[denverappraiser]

Hearts on Fire calls their goods 'the worlds most perfectly cut diamond' and advertises this heavily. I agree that this is pure puffery in the same way that BMW makes 'the ultimate driving machine' but that's where people are getting the word 'perfect' as associated with Hearts and Arrows cuts.